1. Field of the Invention
The invention relates to a resin-molded component that includes a flange having a through-hole.
2. Description of the Related Art
Japanese Patent No. 2643774 discloses a resin intake manifold for an internal combustion engine, in which concave portions may be formed in the flanges of the intake manifold by reducing the thickness of a resin material, in order to reduce the weight of the intake manifold. FIG. 9 is a schematic diagram showing part of the intake manifold disclosed in Japanese Patent No. 2643774. As shown in FIG. 9, in the intake manifold, an intake passage 110 is provided, and a through-hole 130 is formed in the flange 120.
Concave portions 140 and 145 are formed on the surface of the flange 120, the surface facing a cylinder head (not shown) when the flange 120 is fitted to the cylinder head. Each of the concave portions 140 and 145 is formed between the intake passage 110 and the through-hole 130 by reducing the thickness of the resin material. FIG. 10 is a sectional view taken along line X-X in FIG. 9. As shown in FIG. 10, the resin material in the bottom portion 142 of the concave portion 140 and the resin material in a wall 144 of the concave portion 140 are of the same thickness DS.
With this structure, it is possible to reduce the weight of the intake manifold by reducing the thickness of the resin material at portions that do not need to be thick, while maintaining rigidity of the intake manifold.
To mold a resin component, a pressurized molten resin material is injected into a die. The arrows in FIG. 11 show the direction of flow of the molten resin material during the molding of the intake manifold. A thicker arrow indicates the flow of a greater quantity of the molten resin material.
As shown in FIG. 11, the resin material in each of portions corresponding to the locations indicated by arrows a11 and a12 would be thicker relative to the other portions of the flange after molding is completed. That is, a sectional area of the flowing molten resin material is large in each of the portions indicated by the arrows a11 and a12. Therefore, a flow amount of the molten resin material is relatively large in each of the portions indicated by the arrows a11 and a12.
In contrast, the resin material in each of portions corresponding to the locations indicated by arrows b11 and b12 would be thinner relative to the portions of the flange after molding is completed. That is, a sectional area of the flowing molten resin material is small in each of the portions indicated by the arrows b11 and b12. Therefore, the flow amount of the molten resin material is relatively small in each of the portions indicated by the arrows b11 and b12. Also, as shown in FIG. 10, the resin material in the bottom portion 142 of the concave portion 140 and the resin material in the wall 144 of the concave portion 140 both have the same thickness DS. Therefore, the flow amount of the molten resin material is relatively small in each of the bottom portions of the concave portions 140 and 145 indicated by arrows c11 and c12 in FIG. 11.
As shown in FIG. 11, the flow of the molten resin material follows the paths indicated by arrows d11 and d12 and passes along the periphery of the through-hole 130 until the paths meet each other. The resin material in each of the portions indicated by arrows d11 and d12 have are relatively thin after molding is completed. Therefore, the flow amount of the molten resin material is relatively small in each of the portions indicated by the arrows d11 and d12.
FIG. 12 shows the view from the perspective indicated by the arrow A, in FIG. 11, of the portion of the flange at which the flows of molten resin material along the periphery of the through-hole meet. A weld line 150 is formed at the portion of the flange at which the flows of the molten resin material along the periphery of the through-hole meet. After the resin material has hardened, the rigidity of the resin material along the weld line tends to be reduced, as compared to other portions. Further, since the flow amount of the molten resin material is relatively small in each of the portions indicated by the arrows d11 and d12, this tendency becomes still more evident.